This invention relates generally to a Geneva drive, and more particularly to an improved Geneva drive where the input shaft is accurately prepositioned to impart rotation to the output shaft at a predictable time upon rotation of the input shaft.
A well known mechanism for converting rotary motion into intermittent or stepped rotary motion is commonly referred to as a Geneva drive. Geneva drives are particularly applicable for use in machines in which incremental movement of a part of such machine in one direction, or in reversible directions, is desired. Such incremental movement is effected by the intermittent or stepped rotary motion of the output shaft of the Geneva drive. To accomplish such output shaft motion, the Geneva drive includes an input member, rotatable about an axis, having at least one activating element. Upon rotation of the input member, the element is sequentially engaged with radial notches formed in a member concentrically mounted on the output shaft to incrementally rotate the output shaft.
To ensure that the output shaft is smoothly rotated only during the periods of engagement of the element with the notches, the member mounted on the output shaft includes concave portions formed between the radial notches. Such concave portions are engageable by a mating cylindrical surface portion (concentrically mounted on the input member) when the element is not in engagement with the radial notches. The engagement of the concave portions and mating cylindrical surface portion locks the output shaft against rotation (see, for example, U.S. Pat. Nos. 3,605,517, issued Sept. 20, 1971 in the name of Seragnoli, or 3,638,510, issued Feb. 1, 1972, in the name of Staller). While such Geneva drive arrangements provide smooth incremental movement of the output shaft, they do not provide for repeatable and predictable alignment of the element with the notches to establish an accurate relationship therebetween where incremental rotation of the output shaft can be accomplished at a readily predictable time.